A typical Nd:YAG laser produces a beam with a wavelength of 1.064 microns. A second harmonic of this fundamental wavelength has a wavelength of 0.532 microns and a fourth harmonic has a wavelength of 0.266 microns in the ultraviolet region of the spectrum.
There is a commercial need to obtain laser outputs of relatively high power at these latter, shorter wavelengths, or even at still shorter wavelengths.